Commutator with one anchor location



Dec. 2.3, 1969' J. STUDE ET AL 3,486,057

CCMMUTATOR WITH ONE ANCHOR LOCATION Filed April 2, 1968 FIG. 2

WITNESSES Q INVENTORSV mfl md John v. S1ude Clayton EAlliso 1 .7 BY 6 1,

ATTO RN Y Y US. Cl. 310-235 4 Claims ABSTRACT OF THE DISCLOSURE A commutator for a rotating machine, the commutator comprising segments or bars with each segment having one anchor location on a high strength insulating bushing in an area axially adjacent the armature connecting riser of each segment.

BACKGROUND OF THE INVENTION The invention relates generally to commutators for dynamoelectric machines, and particularly to the shrink ring type of commutator where the commutator bars or segments are fixed on a bushing or shaft by a heavy shrink fit of banding material.

In the design and construction of such commutators for rotating machines, the segments or bars comprising the commutator must be held firmly in place on a supporting insulating bushing in order to prevent the bars from coming loose and moving as a result of commutator rotation and the centrifugal forces attendant therewith, and to prevent the armature connecting riser of each bar from breaking as a result of bar movement. However, the commutating bars should also have a degree of flexibility so that portions thereof can move axially along the bushing with changes in temperature, which changes cause thermal expansion and contraction of the bars.

Heretofore, the concern of the prior art has been primarily with rotational stability of the bars to the neglect of axial or lateral flexibility. Thus, the bars have been secured to the insulating bushing and shaft with heavy shrink fits along substantially the entire length of the bars so that the amount of lateral expansion of the 'bars, due to temperature increases, has been essentially nonexistent. As a result, when the temperature in the machine and commutator rises, the bars expand against the securing bands and against the insulation separating the bars to the extent that the bars twist and buckle against the bands and the insulation, and the armature connecting risers of the bars move and thereby tend to break.

BRIEF SUMMARY OF THE INVENTION The present invention comprises a simple structure which provides both rotational stability and lateral flexibility for commutator bars or segments in an economical and efficient manner. Briefly, the structure comprises a supporting bushing made from a high strength insulating material, the bushing having an annular raised portion or boss formed on its outer periphery, and an accommodating or mating slot or recess provided in each of the commutator bars. The depth of the recess is slightly less than the height of the boss so that when the commutator is banded on the bushing a heavy shrink fit will result only in the area of recess and boss, which area forms a single anchor location for each bar. The remainder of the bar is thus free to move axially since the remainder of it is secured to the bushing by a fit substantially lighter than that at the anchor location.

The boss and slot are located axially in the area of the armature connecting riser of each of the bars so that the riser is held firmly in place while the remainder of the bar is allowed to move. In this manner, the riser is *nited States Patent 3,486,057 Patented Dec. 23, 1969 ICC prevented from breaking and the remainder of the bar prevented from expanding circumferentially and radially against the bar insulation and securing bands.

THE DRAWINGS The invention, and the objects and advantages will be better understood from consideration of the following detailed description read in connection with accompanying drawings, in which:

FIGURE 1 is a partial side elevation view and longitudinal section of a commutator constructed in accordance with the principles of the invention; and

FIG. 2 is an enlarged view of a portion of the commutator shown in FIG. 1.

PREFERRED EMBODIMENT Specifically, there is shown in FIG. 1, a commutator generally designated 10 comprising a plurality of bars or segments 12 disposed about the outer surface 13 of an insulating bushing 14. The bars are separated and insulated from each other by thin insulating sheets of material 15 such as mica disposed between adjacent bars. When the bars and sheets are placed together they form a cylindrical commutator shell generally designated 16.

The bushing 14 is shown disposed on a metal bushing 17 fixed on a shaft 18 of a machine rotor not shown. Each of the bars is provided with a radially extending riser 20 for connection with armature windings not shown.

In accordance with the invention, the bushing 14 is made from a high strength, insulating material, for example a glass woven laminate with a resin impregnated bond, and provided with an annular raised portion or boss 22 on its outer surface 13 at an axial location beneath the armature connecting riser 20 of each of the bars 12. The annular boss 22 may be machined or otherwise formed on the high strength bushing 14.

In a similar manner, each of the commutator bars 12 is provided with a slot or recess 24 in the inner surface 25 thereof for receiving the annular boss 22 on the bushing 14 when the commutator bars are placed thereon. When the bars are placed together to form the commutator shell 16, the individual recesses 24 form an annular recess.

The commutator 10 is assembled by first curing the insulating bushing 14 on the metal bushing 17, or on the shaft 18 if a metal bushing is not used, and then forming the annular boss or raised portion 22 thereon. The bushing is cured by a suitable process to give the bushing its high strength characteristic mentioned above.

The commutator bars 12 and the insulating sheets 15 are placed together to form the cylindrical shell 16 for disposal on the bushing 14. The shell is first, however, machined or otherwise formed to provide annular recesses 28 in the outer periphery 29 thereof to accommodate clamping rings or bands 30 disposed therein as shown in the figures.

The bands 30 are formed about the shell 16 in a manner to clamp and compress the commutator bars 12 and the insulating sheets 15 together to form an inner shell diameter similar to the outer diameter of the bushing 14. The bands 30 may be made from a resin impregnated Woven glass tape, and cured to form a high strength insulating material similar to that of the bushing 14 though the invention is not limited thereto.

The commutator shell 16, as formed and described above, is now disposed on the insulating bushing 14 in a manner to provide a heavy shrink fit about the annular boss 22 of the bushing, and a lighter fit about the remaining portion of the bushing. This is accomplished by forming the annular boss 22 to have a height dimension larger than the depth dimension of the recess 24 provided in each of the commutator bars, as shown in FIG. 2, and the diameter dimensions of the remaining portions of the shell and bushing are chosen to provide the light fit when the shell is suitably located on the bushing. The dimensional difference between the boss 22 and the recess 24, as depicted in FIG. 2, is somewhat exaggerated, the difference depending upon the overall size of the commutator 10.

To fit the commutator shell on the bushing, it is first heated to expand its inner diameter so that it can be slipped on the bushing 14, and the annular recess (formed by the combined recesses 24 in the bars) positioned to receive the annular boss 22. As the commutator shell 16 cools, it shrinks on the insulating bushing to form a heavy shrink fit on the annular boss 22. This anchors the commutator bar 12, and thus the entire shell 16, on the boss 22 which is axially disposed in the area of the riser 20 of each bar.

Thus a single anchor location is formed for each of the bars 12 which is axially limited to the boss and slot arrangement 22, 24 as described. With temperature conditions causing thermal expansion of the bars, the portion of each bar in the area of riser 20 remains substantially fixed while the remainder of the bar is free to move axially along the remainder of the bushing surface 13 because of the lighter fit existing between the remainder of the bar and bushing. In this manner, the riser 20 is prevented from moving and thereby break- A sealant material (not shown) may be employed at the ends of the bars 12 and the outer surface of the insulating bushing 14 to seal the engaging surfaces of the bars and bushing against dust and other foreign matter.

For a similar reason, the insulating bushing 14 is shown provided with an annular pointed projection 32 which functions as a dust thrower and provides extra creepage distance between the end of the commutator bars 12 and the metal bushing 17.

It should now be apparent from the foregoing description that a new and useful commutator bar anchoring arrangement has been disclosed wihch anchors the bar at one location While remaining portions of the bar are free to move axially along the outer surface of a high strength insulating bushing with thermal expansion and contraction of the bars. The anchor location is axially adjacent a radial riser portion of the bar employed for armature connection, the riser portion thereby prevented from breaking due to movement of the bar. The single location anchoring arrangement is economically provided by simple use of an annular raised portion formed on the high strength insulating bushing and an annular accommodating recess formed when the commutator bars, with their individual recesses, are disposed together to form a commutator shell.

Though the invention has been described with a certain degree of particularity, it should be noted that changes may be made therein without departing from the spirit and scope thereof.

What is claimed is:

1. A commutator comprising an insulating bushing made from a high strength insulating material,

a plurality of commutator bars or segments disposed on said bushing,

said bars and said bushing having respectively inner and outer mutually engaging surfaces, said surfaces being provided with a mating recess and boss arrangement for mutual engagement,

the depth dimension of said recess being less then the height dimension of said boss, and

each of the bars having radially extending riser located in an area axially adjacent that of said slot and boss arrangement,

' said commutator being fitted on said bushing in a manner providing a heavy shrink fit only in the area of said recess and boss arrangement.

2. The commutator recited in claim 1 in which the mating recess and boss arrangement comprises an annular raised portion formed on the outer, bar

engaging surface of the bushing, and

a recess provided in the inner, bushing engaging surface of each of the bars.

3. The commutator recited in claim 1 in which the bars and bushing are mounted on the rotor shaft of a dynamoelectric machine.

4. The commutator recited in claim 1 in which the insulating material of the bushing is a cured, resin impregnated glass cloth laminate.

References Cited UNITED STATES PATENTS 1,274,411 8/1918 Halbleib et al. 3l0236 1,287,309 12/1918 Hensley 310 235 2,896,100 7/1959 Axelson 310-271 MILTON O. HIRSHFIELD, Primary Examiner L. L. SMITH, Assistant Examiner US. Cl. X.R. 

